1. Field of the Invention
The present invention relates to a tire vulcanizing mold in which a sipe blade for forming a sipe on a tire surface are provided on a surface of the mold, a sipe blade, and a method of manufacturing the sipe blade.
2. Description of the Related Art
Conventionally, in order to prevent slipping of a vehicle on an icy road, or the like, there has been known a technique for providing a plurality of sipes (i.e., shallow cuts) on a tire surface. Among these sipes, there is a sipe of a desired shape formed so as to prevent occurrence of a crack in a tire from a sipe bottom portion.
As a technique relating to formation of such a sipe, there have been disclosed a tire vulcanizing mold described in Japanese Patent Application Laid-Open (JP-A) No. 2-200406 and a sipe blade described in Japanese Patent Application Laid-Open (JP-A) No. 4-215507.
The technique disclosed in JP-A No. 2-200406 has a structure in which a free end of a sipe blade provided on a tire-molded surface of the vulcanizing mold is only folded back and a stepped portion is formed at a position of a folded end of the sipe blade. For this reason, when the mold is separated from the tire after vulcanization, rubber compositions are caught by the stepped portion due to the rubber compositions flowing in vicinities of the stepped portion during vulcanization of a tire. Thus, smooth separation of the mold from the tire has not been achieved. Further, when a desired mold is formed in the sipe blade, for example, when a mold is formed in a direction perpendicular to a direction of the sipe blade being folded back, a cross-sectional configuration of the sipe-blade folded portion locally deforms due to insufficient strength of the folded portion. As a result, the sipe may not be formed in a desired shape.
Further, the technique disclosed in JP-A No. 4-215507 has a structure in which an axial pin is inserted in an inner side of the folded portion of the sipe blade, and has a drawback in that a manufacturing cost of the sipe blade rises due to an increase in the number of parts. Further, with this structure, the sipe blade is bent with the axial pin being used as a core member of the bent portion thereof, so that the shape of the bent portion conforms to that of the axial pin. Accordingly, in order to accurately manufacture all of the sipe blades used for the entire mold, all the axial pins must be accurately machine-processed. Even in this case, the manufacturing cost rises.